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Building Science

The Water Efficiency Rating Score (WERS)

The Green Builder Coalition’s new tool is ready

Reading the rated water flow in gallons per minute and then measuring the flow are both part of the Water Efficiency Rating Score process.
Image Credit: Energy Vanguard
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Reading the rated water flow in gallons per minute and then measuring the flow are both part of the Water Efficiency Rating Score process.
Image Credit: Energy Vanguard
Measuring structural waste is one part of the WERS inspection.
Image Credit: Energy Vanguard
Checking the irrigation controller is part of the WERS inspection process for outdoor water use.
Image Credit: Energy Vanguard
A screenshot of part of the WERS inspection checklist for indoor water efficiency
Image Credit: Green Builder Coalition
A diner in the Southwest, where I had a nice lunch with Steve Onstad
Image Credit: Energy Vanguard
The California drought is having a big effect on people and businesses out West.
Image Credit: Energy Vanguard

The Green Builder Coalition has been working hard on their Water Efficiency Rating Score — the WERS — for homes. The inaugural WERS training happened in Santa Fe, New Mexico, in March. I was in that class, and I learned a lot.

The program has been in development for the past couple of years. Now it’s ready for prime time.

How the program works

Like the HERS Index for energy efficiency, the WERS is a way to put a number on a home’s water efficiency. It’s a water use modeling tool that allows you to compare one house to another. You have to put in all the data for a home’s water use, and the tool gives you a number, generally between 0 and 100. As with the HERS Index, lower is better. A WERS of zero means you’ve got a net zero water house. That happens only when you capture rainwater.

One of the things you do is measure structural waste. That’s the amount of water that comes out of a faucet or shower while you’re waiting for the hot water to arrive. The photo below (see Image #2 at the bottom of the article) shows the equipment we used in the class to measure water for a shower. It consists of a Ziploc bag, a piece of PVC pipe with a couple of fittings to hold the bag, and a measuring cup. This setup works really well!

When you’re doing a field inspection, you go around and fill out the checklist. The screenshot in Image #4 (below) shows part of the checklist for indoor water efficiency. The first thing you do is put a pressure gauge on a faucet, turn off the water supply to the house, and see if the pressure drops. That tells you if you have leaks. (Of course, you have to make sure no one flushes a toilet or turns on any water during the test.)

What really distinguishes WERS, though, is that it includes both indoor and outdoor water use. That’s not true for HERS and energy. A HERS Index, for example, doesn’t include the energy use of swimming pools, hot tubs, snowmelt systems, or garage heating and cooling. And those can be huge!

The WERS tool generates a score for indoor water use, outdoor water use, and a combined score for both. Another great thing about WERS is that you get credit for capturing rainwater and graywater. This is similar to lowering your HERS Index by having photovoltaics on the roof of your house contributing to your energy supply.

Highlights of my WERS training

I’ve been traveling to Santa Fe each year for the past three years for various events. It’s a great community with great home builders, HERS raters, and an active Passive House contingent. Plus I get to hang out with a guy with a woman’s name (Kim Shanahan), see my trainer friend Amanda Hatherly (who only lives in places that start with “New”), and go to lunch at fantastic roadside diners (see Image #5, below) with HERS rater Steve Onstad.

Let’s talk about water now. That was my reason for taking to the WERS class after all. They don’t have much of the stuff in New Mexico, as you might surmise from Image #6, below. But it’s not just a dry climate thing. Water’s a huge issue in Atlanta, too, where we get more than 50 inches of rain each year. (The state of Georgia got sued by Alabama and Florida a while back for using water they thought should have flowed down to them.)

In the WERS class, the trainers gave us background info on water use, codes, and laws. Colorado, for example, is the only state where it’s illegal to capture rainwater. New Mexico, on the other hand, is the only state that has a law making surface water and groundwater equal.

The instructors were David Dunlap and Doug Pushard. Those two guys have a wealth of knowledge on water efficiency. Dunlap is a builder; he covered the indoor water use material. Pushard has a rainwater harvesting company; he helped us understand outdoor water use.

The indoor water efficiency was all pretty straightforward and easy for me. The outdoor water efficiency wasn’t so easy. Let me just say that you might want to have someone who knows plants around if get into doing WERS. In determining the outdoor water use, you have to classify the plants as low, medium, or high water use.

One product the instructors told us about really caught my eye. Behavioral waste, as opposed to the structural waste, is the water that gets wasted when someone turns on the water in the shower and goes away for 10 minutes while it gets hot. Evolve Technologies has products that can reduce that waste significantly. When you turn on the faucet or the shower, it flows at full capacity until the water gets hot. Then it slows to a trickle until the person is ready to use it.

Overall, the WERS training was fantastic. It’s a powerful tool that can help us solve problems. The class I attended in Santa Fe sold out, so they’ve scheduled another one for June, also in Santa Fe.

I think you’ll be hearing more and more about WERS. Water is a huge issue. The drought in California, for example, is having a huge effect on people and businesses there. The WERS is a great tool to help as we get more serious about water conservation.

Allison Bailes of Decatur, Georgia, is a speaker, writer, energy consultant, RESNET-certified trainer, and the author of the Energy Vanguard Blog. Check out his in-depth course, Mastering Building Science at Heatspring Learning Institute, and follow him on Twitter at @EnergyVanguard.


  1. Jonathan Lawrence CZ 4A New Jersey | | #1

    Thanks for the info.


    Thanks for the info. One more index I need to think of on my next build.

    I recently installed an Evolve showered in the master bath of my current house. This shower is a nightmare as it is about 70 feet from the hot water heater and the piping runs in the ceiling above the garage. The Evolve works as advertised and as soon as hot water arrives, the flow slows to a trickle until you pull the rip cord.

  2. User avater GBA Editor
    Allison A. Bailes III, PhD | | #2

    Response to Jonathan Lawrence
    Glad to hear your Evolve shower performs well. I haven't seen them in action but really like the idea.

  3. Daniel Beideck | | #3

    I also have a Evolve showerhead that I really like. In addition to the water (and energy) savings, there are other advantages. Because you can hear the water flow change as soon as it's warm, you are free to do other things while waiting for the shower and still know the instant it's ready. It's not a big deal if what you're doing takes a little longer than it took the shower to get warm since the flow is very minimal once it is warm until you pull the cord.

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